1. Field of the Invention
The present invention relates to an electronic climate control system suitable for use in automotive vehicles, and specifically to an electronic climate control system for an air conditioner with a by-pass door through which cooler air conditioner system air is directed to instrument panel/dash air ducts or discharge outlets, and an actuator serving to open or close a hot-water valve as well as the by-pass door.
2. Description of the Prior Art
In recent years, there have been proposed and developed various automated electronic climate control systems that control the heating, ventilation, and air conditioning systems within the passenger compartment. On modern automobiles, the mechanic/technician in the field have made efforts to provide a more complete bi-level mode. To ensure the more complete bi-level mode, the today's motorcar often employs a by-pass passage that is capable of delivering cool air flowing through an evaporator core directly to instrument panel/dash air ducts or discharge outlets such as side vents and center vents. The use of such a by-pass passage can ensure a forcible discharge of cool air through the by-pass passage to the discharge outlets with a by-pass door (usually provided at the outlet of the by-pass passage) opened. For the purpose of reducing the number of parts constructing an automobile air conditioner, the opening or closing action of the by-pass door and the opening or closing action of a hot-water valve (or a hot-coolant flow control valve that controls the engine coolant flow through a heat-exchanger core) are both done by means of a single actuator mechanically linked to both the by-pass door assembly and the hot-water valve unit. Usually, the single actuator is designed to fully close the hot-water valve when the by-pass door is fully opened. Referring to FIG. 5, there is shown a typical by-pass door opening/closing procedure programmed into a prior art electronic climate control system. In accordance with the by-pass door control procedure shown in FIG. 5, in step S20, Input information is read. The input information comprises various parameters such as a discharged-air outlet mode (simply discharge mode) selected by a mode select switch, a set in-car temperature selected by a vehicle occupant by rotating or sliding a temperature selector switch or dial, an in-car temperature (or a room temperature in the vehicular cabin), an outside (ambient) air temperature, an amount of insolation (or a sunload temperature), a current value of an opening of the by-pass door, a current value of an opening of an air-mix door, and the like. Thereafter, in step S21, a test is made to determine whether a mode-selection switch is positioned in a VENT mode. When step 21 determines the VENT mode, step S28 proceeds in which a test is made to determine if a so-called full-cool mode is selected. When the answer to step S28 is affirmative (YES), step S29 enters in which a by-pass door is fully opened to direct cool air leaving the evaporator core via the by-pass passage to plural ventilator ducts or nozzles. Conversely, when the answer to step S28 is negative (NO), step S30 enters in which the by-pass door is fully closed to block cool-air flow through the by-pass passage. In case of any operational mode (e.g. a DEFROST mode or FOOT mode) except the VENT mode, a target in-car temperature and a temperature deviation Sb between the target in-car temperature and a temperature of actual discharged air are both calculated in accordance with predetermined expressions respectively at steps S22 and S23. Thereafter, through a decision diamond S24, the opening or closing action of the by-pass door is controlled on the basis of the temperature deviation Sb. Concretely, in step S24, a test is made to determine whether the temperature deviation Sb (obtained through step S23) is greater than a predetermined upper threshold such as +2.degree. C., or less than a predetermined lower threshold such as -2.degree. C., or the temperature deviation Sb is within a deviation ranging from the predetermined lower threshold to the predetermined upper threshold. In case of Sb&gt;+2.degree. C., that is, when the in-car temperature sensed is less than the target in-car temperature, step S25 proceeds in which the bypass door is shifted towards its closed position. In case of .vertline.Sb.vertline..ltoreq.2.degree. C., (-2.degree. C..ltoreq.Sb.ltoreq.+2.degree. C.), that is, when the in-car temperature sensed is almost equivalent to the target in-car temperature, step S26 proceeds in which the angular position of the by-pass door is maintained unchanged. In case of Sb&lt;-2.degree. C., that is, when the in-car temperature sensed exceeds the target in-car temperature, step S27 proceeds in which the by-pass door is shifted towards its full-open position. The routine shown in FIG. 5 is repeatedly executed as time-triggered interrupt routines to be triggered every predetermined sampling time intervals, so as to control the discharged-air temperature towards the target in-car temperature. According to the by-pass door control procedure of FIG. 5, under a particular condition that a value of the deviation Sb continues to be below the lower threshold (e.g. -2.degree. C.), the by-pass door also continues to shift towards its full-open position. In such a case, in the event that the air conditioning system employs a single actuator connected to both a linkage of the hot-water valve and a linkage connected to the by-pass door for opening or closing action of the hot-water valve as well as the by-pass door, the hot-water valve remains closed with the by-pass door continuously kept at its full-open position, thereby shutting off hot-water supply into the heater core for a while. However, during the actual driving, the driver or vehicle occupant will often require any warm-air flow within towards the passenger compartment such as front foot vents or rear foot vents, under the previously-noted particular condition (with the by-pass door maintained at its full-open position for a while). For example, in case of a so-called BI-LEVEL mode at which the driver/passenger requires both cool-air flow through face ventilator ducts or nozzles (such as center ventilator ducts and side ventilator nozzles) and warm-air flow through foot vents (or floor outlets), it is unpreferable to shift to the fully-closed position of the hot-water valve in synchronization with shifting of the by-pass door to its full-open position. Similarly in case of a so-called DEFROST mode, it is required to provide both warm-air flow through defrost outlets such as side defroster dusts and front defroster nozzles and cold-air flow through ventilator ducts or nozzles, for the purpose of preventing any moist air from clouding the windshield and of preventing breath humidity from the driver or passengers and of removing moisture within the passenger compartment. As set forth above, according to the by-pass door control procedure of FIG. 5, since the hot-water valve is fully closed while the by-pass door is held in the full-open position, the system cannot provide a desired warm air flow from the foot vents or defroster ducts or nozzles for example in the BI-LEVEL mode and the DEFROST mode. That is to say, the conventional system as shown in FIG. 5 cannot satisfactorily provide cold and warm air flows desired.